Retinoic acid affects the organization of reticulospinal neurons in developing Xenopus

The effects of all-trans retinoic acid (RA) on the differentiation of the reticulospinal system were studied in Xenopus. RA was applied in concentrations of 10(-5) and 10(-6) M for 30 min at stage 12. When siblings had reached stages 46-48, the spinal cord was transected in anesthetized control and experimental animals and the reticulospinal cells were visualized through retrograde transport of fluorescing dextran amines. The lower concentration of RA led in many animals (22%) to the formation of multiple Mauthner-like cells. Higher concentrations resulted in the formation of two uninterrupted longitudinal columns of rather uniform reticulospinal cells. These data suggest that the normal expression of Hox genes pattern--known to be altered by RA--may be necessary for the differential specification of compartments of the reticulospinal system.